Binding and receptor-mediated endocytosis of pregnancy zone protein-proteinase complex in rat macrophages.

125I-labelled pregnancy zone protein complex was injected intravenously in rats and after 6 min uptake into cells of the liver and spleen was determined by electron microscopic autoradiography. The liver took up 68% of the injected radioactivity; 61% was in the hepatocytes and 7% was in the liver macrophages (Kupffer cells). The spleen took up 3-4% and nearly all the radioactivity was in the macrophages of the red pulp.

Evidence for binding of human pregnancy zone protein-proteinase complex to alpha 2-macroglobulin receptors.

125I-labelled human pregnancy zone protein complexed with chymotrypsin was removed from the circulation with a half-time of 2.3 min after intravenous injection in rats. After 6 min about 67% of the label was present in the liver and about 3% was in the spleen, both in male and in female pregnant rats.